Adam Rooney's scored twice as Birmingham cruised through to the fifth round of the FA Cup, ending Sheffield United's eight-match winning run at Bramall Lane.

The 23-year-old struck seven minutes before half-time, after the Birmingham teenager Nathan Redmond had scored against the run of play in the 18th minute.

Birmingham never looked back after Rooney had scored the second goal, and although the Blades struck the woodwork twice in a matter of seconds shortly after the restart, Wade Elliott scored a third for the Championship side and Rooney wrapped up the contest in the 78th minute.

Danny Wilson's Blades are flying high in League One as they bid to bounce straight back to the second tier. But they were no match for Chris Hughton's in-form side, who have now won their past five matches and are unbeaten in their past nine.

United were unchanged for the fourth game running, but Hughton recalled goalkeeper Colin Doyle, midfielders Morgaro Gomis, Redmond and Elliott, plus striker Rooney.

The tie's opening chance fell to the Blades in the fourth minute. The full-back Matt Lowton crossed from the right and midfielder Kevin McDonald's well-struck shot from the edge of the penalty area was blocked by the defender Curtis Davies.

Ched Evans was next to threaten as United made all the early running but Birmingham shocked them by taking the lead. The midfielder Jordan Mutch swung over a corner from the right and when the ball broke to Redmond on the edge of the area, the 17-year-old rifled home a low shot into the centre of goal.

Redmond fired another effort just wide when cutting in from his wing five minutes later, as Birmingham seized the initiative but Blades striker Evans forced Doyle into a smart save with a 20-yard free-kick in the 27th minute.

But, buoyed by their first goal, Birmingham carried all the momentum and when they doubled their lead through Rooney it was no more than they deserved. The winger Chris Burke waltzed into the area and played the ball square for Rooney to hit home his fifth goal of the season.

The Blades had chances to get back into the game seven minutes after the restart but luck was not on their side. Lee Williamson's crisp shot from inside the area hit the crossbar and Lowton's follow-up effort also came back off the woodwork, with Doyle well beaten.

Elliott rubbed salt into Blades' wounds when thundering home Birmingham's third goal from 20 yards five minutes later. Rooney sidefooted home the fourth goal following David Murphy's cross.